The initial objectives of this project were to use human adenoviruses and adenovirus-SV40 (Ad2-SV40) recombinants as tools to study the genetics of DNA tumor viruses, to define the role of viral genes and viral antigens in viral oncogenesis and to study the biology of Ad2-SV40 recombinants. Due to the lack of proper containment facilities in NIAID between January 1973 and May 1978, there was a 5-year disruption (see past reports) in the major thrust of this project. During this interval, a study of Ad2-SV40 recombinants associated tumor induction in Syrian hamsters by these agents with the incorporation into the adenovirus-2 chromosome of a specific segment of SV40 DNA. To begin to understand the mechanisms by which this SV40 DNA segment conveys oncogenicity to these recombinants, it was necessary to understand why Ad2 was nononcogenic and why SV40 was highly oncogenic for hamsters. Since Ad2 and SV40 can transform hamster cells in tissue culture, we initiated a study of the oncogenic properties of cells transformed by these viruses. The results thus far lead us to believe that SV40 conveys to transformed hamster cells the ability to resist rejection by the host's cellular immune system.